Dear forum members,

Im involved on Exchange cross forest migration between Exchange 2010 and other forest with Exchange 2013. I have designed migration phases, currently have installed and configured Exchange 2013 new environment and finishing some details with Forest trust, but I have one question about calendar.
Source Exchange have about 20 authoritative domains that must to be on destination forest, and of course calendar must be accesible on both Exchange forest. I try to create a federation trust to share calendar, but How can I do when sorce and destination are same domains? Since we are talking about 2000 mailboxes, forest coexistence will be long enough users ask about calendars of migrated users. Must to configure all domains on destination forest as federated domains or as authoritative?

Any input and detailed steps are welcome.

You have to ensure that each side has a unique domain.  Both can share the same domain for recipients as secondary addresses, but that can't be the one that's federated.

Hi,

Great advice from Ed.

As an additional, here's an article about "Exchange Queue & A: Across the Forest", for your reference:
https://technet.microsoft.com/en-us/magazine/hh641445.aspx

"This is a somewhat complex topic, but you essentially have the following options:
Use the Microsoft Federation Gateway (MFG) service
Use the Exchange Availability service"